The present invention relates to a process for producing a deionizing resin by reacting with a fiber-forming organic compound having at least one reactive hydroxy group or amino group, an organic compound having at least one reactive hydroxy group and at least one active chelating site. Further, the present invention relates to a process for removing metals from such a deionizing resin and using it to remove metals from aqueous and non-aqueous systems.
The present invention relates to a process for producing a deionizing resin by reacting a polymeric organic compound having at least one reactive hydroxy group and at least one active chelating site, with a fiber-forming organic material having at least one reactive --OH or --NH.sub.2 group, such as cellulose, rayon (regenerated cellulose), poly(vinyl alcohol), a copolymer of divinyl benzene and hydroxystyrene, poly(ethylene terephthalate), nylon 6 (polycaprolactam, nylon 66 (polyhexamethylene adipamide). The present invention further relates to a process for removing metals from such a deionizing resin by washing the reaction product with an acid, such as 1-25% mineral acid, and using it to remove metals from aqueous and non-aqueous systems, such as photoresists and components of photoresists.
Photoresist compositions are used in microlithorgraphy processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolete (UV) light electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.
Metal contamination has been a problem for a long time in the fabrication of high density integrated circuits and computer chips, often leading to increased defects, yield losses, degradation and decreased performance. In plasma processes, metals such as sodium and iron, when they are present in photoresists, can cause contamination especially during plasma stripping. However, these problems have been overcome to a substantial extent during the fabrication process. For example, by utilizing HCl gettering of the contaminants during a high temperature anneal cycle.
As semiconductor devices have become more sophisticated, these problems have become much more difficult to overcome. When silicon wafers are coated with a liquid positive photoresist and subsequently stripped off, such as with oxygen microwave plasma, the performance and stability of the semiconductor device is often seen to decrease. As the plasma stripping process is repreated, more degradation of the device frequently occurs. A primary cause of such problems has been found to be the metal contamination in the photoresist, particularly sodium and iron ions. Metal levels of less than 1.0 ppm in the photoresist have been found to adversely affect the properties of such semiconductor devices.